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Design of O-Ring Seals.

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Presentation on theme: "Design of O-Ring Seals."— Presentation transcript:

1 Design of O-Ring Seals

2 Design of O-Ring Seals Primary Source of information

3 Why O-Rings? Can be used for static and dynamic applications
Compact – need very little space - light weight Easy to incorporate into design Do not require high accuracy Simple design rules Easy to install or remove Easy to service Available in many standard sizes, materials

4 Why O-Rings? Wide range of operating temperatures
Wide range of operating pressures Good durability and abrasion resistance Many O-ring materials for a wide range of chemicals Their failure or deterioration is gradual Inexpensive

5 Limitations of O-rings
Temperature (typically between -40 and 400 degrees F) Rotary speeds ( not to exceeding 1500 feet per minute) For a 2 inch shaft, it is 3000 rpm Vulnerable to sharp edges Require small clearances

6 O-Rings

7 Popular O-ring materials
Nitrile (Buna-N) Variety of trade names Copolymer of butadiene and acrylonitrile Most widely used and economical elastomer Temperature Range: Standard Compound: -40° to +257°F Hardness (Shore A): 40 to 90

8 Popular O-ring materials Nitrile (Buna-N)
Excellent resistance to petroleum-based oils and fuels silicone greases hydraulic fluids water and alcohol High tensile strength High abrasion resistance

9 Popular O-ring materials Nitrile (Buna-N)
Applications Oil resistant applications Low temperature uses Off-road equipment Automotive, marine, aircraft fuel systems

10 Other O-ring Materials
Viton® / FKM:  Fluorocarbon (Viton®) exceptional resistance to chemicals, oils, temperature extremes (-13°F to +446°F), low compression set. Applications include: aircraft engines, automotive fuel handling systems, and chemical processing industries. Ethylene-Propylene / EPDM:  EPDM has excellent resistance to heat, water and steam, alkali, mild acidic and solvents, ozone, and sunlight with a temperature range of (-40ºF to +275ºF); but it is not recommended for gasoline, petroleum oil and grease, and hydrocarbon environments.

11 Other O-ring Materials
Fluorosilicone / FVMQ:  Fluorosilicone (-75º to +400ºF) combines the good high and low temperature stability of silicones with the fuel, oil, and solvent resistance of fluorocarbons. FVMQ is used for aerospace fuel systems, auto fuel emission control systems. However, due to relatively low tear strength, high friction and limited abrasion resistance of these materials, they are generally not used in dynamic applications.

12 Other O-ring Materials
Silicone / VMQ:  Superior as static seals in extreme temperature conditions. Standard compounds handle operating temperatures -85º to +400ºF. Silicone compounds are popular in food and medical applications because they are clean and do not impart odor or taste. Special Phenyl silicones can be used down to -148°F.

13 Other O-ring Materials
Neoprene® / CR:  Neoprene (-40º to +250ºF) features good resistance to petroleum oils, ozone, sunlight, relatively low compression set, good resilience and physical toughness. It is the preferred sealing material for the refrigeration industry because of its resistance to ammonia and Freon




17 O-Ring Seal Design The O-ring Specifications Size (inside diameter)
1/32 to 26 inches CS (Cross-Section) 1/32 to ¼ inch Rigidity (Hardness) Material

18 O-ring Standards Standard AS568 ISO 3601 Example
AS016-70N Nitrile O-ring (AS Size CS x ID)

19 O-ring Search Tools


21 O-Ring Hardness Measured on Shore-A hardness index
Shore 20A = Rubber Band Shore 40A = Pencil Eraser Shore 60A = Car Tire Tread Shore 70A* = Running Shoe Sole Shore 80A = Leather Belt Shore 100A = Shopping Cart Wheel


23 O-Ring Properties Fluid resistance Hardness Toughness
Volume change (swell / shrinkage) Compression set Thermal effects Resilience Deterioration Corrosion Permeability Coefficient of friction Coefficient of thermal expansion Compression set relaxation Tensile strength Elongation Tear resistance / Abrasion resistance

24 O-ring Seal Design The Gland (Groove + Spacing) Depth of groove
Width of groove Diameter of bore and piston Surface finish Tolerances

25 Static Seals Static Axial Seal (Face Seal)

26 Static Seals Static Crush Seal

27 Static Seals Static Radial Seal (Piston Seal)

28 Dynamic Seals Reciprocating Seals

29 Dynamic Seals Rotary Seals

30 Dynamic Seals

31 General Design Guidelines
Stretch should be less than 5% on the O-ring I.D. Groove depth must be smaller than the O-ring CS O-ring should not completely fill the gland Between 75% and 90% Static seal CS should be compressed from 10% to 40% Dynamic seals should be compressed from 10% to 30%


33 Design of Axial Seal Axial Seal


35 Example Design Design a groove for a 1.5 inch diameter Internal pressure O-ring O-ring : (ID: /- .013) (W: .07 +/- .003) Material: Buna-N Hardness: 70 Shore-A A: (-0 , ) G: .125 (-0, + .01) H: .049 (-0,+.005)

36 Example Design Checking resulting compression
Compression (squeeze) = W - H Min. Comp. = Wmin - Hmax Min. Comp. = in (18.5%) Max. Comp. = Wmax - Hmin Max. Comp. = in (34.3%)

37 Radial Seal Radial Static Piston Seal

38 Example Design Design a groove for a 0.7 inch diameter piston ring
O-ring : (ID: /- .009) (W: .07 +/- .003) Material: Buna-N Hardness: 70 Shore-A A: .746 (-0 , ) B: .745 (-.001, + 0) C: .638 (-.001,+ 0)

39 Example Design Checking compression Also check Comp = W – 0.5(A - C)
Min. Comp = Wmin – 0.5(Amax – Cmin) Min. Comp. = in (17.1%) Max. Comp. = in (26.0%) Also check Extrusion gap Stretch Squeeze


41 Radial Static Rod Seal

42 Static Crush Seal

43 Static Crush Seal

44 Dynamic Seals

45 Gland Design For Dynamic O-ring Seals

46 Reciprocating Motion

47 The O-ring’s O. D. is larger than the cylinder bore diameter
The O-ring’s O.D. is larger than the cylinder bore diameter. Peripheral squeeze is applied to the O.D. as the O-ring is installed into the bore. Incoming air pressure forces the O-ring against the walls sealing

48 Floating O-Rings Advantage Limitations
Greatly reduced breakout friction Longer seal life Limitations Air pressure less than 200 psi in pneumatic cylinders In hydraulic systems small amount of leakage must be permissible Floating O-rings are NOT suitable as rod seals

49 Alternatives to O-Rings U-cup Seals
O-rings have a tendency to roll and move in reciprocating motions U-cups create more sealing as the pressure increases U-cups require less precision for the associated hardware

50 Alternatives to O-Rings U-cup Seals

51 Typical Applications

52 Buffer Seal Buffer seals are one-way seals that protect rod seals from pressure spikes yet allow fluid (lubricant) to reach the main seal

53 Rotary Seals

54 Due to centrifugal force and Gough-Joule effect rotary O-rings are only installed in the housing not on the shaft

55 Gough-Joule effect When an elastomer is stretched and heated, it will contract.

56 Rotary O-Ring Limitations
O-ring seals are NOT recommended for rotary applications under the following conditions: Pressures exceeding 900 psi Temperatures lower than -40° F or higher than 225° F Surface speeds exceeding 600 feet per minute (fpm). 2300 rpm for 1 inch diameter shaft 1150 rpm for 2 inch diameter shaft

57 Rotary Seals

58 Lip Seals Lip seals work well in high speed low pressure rotating shafts

59 Main Application of Lip Seals
Ball and roller bearing protection As little as 0.002% water in lubrication oil can reduce ball bearing life by 50% Solid particles cause rapid damage to the bearing races.



62 The purpose of the spring is to provide a uniform load on the lip
The spring keeps the seal lip in contact with the shaft during higher speeds and also overcomes compression set and wear of the lip material.

63 There is a tendency for liquids to be pumped from the low angle side towards the high angle side. Underneath the flattened area a thin fluid film is formed. Its thickness must be between 1 and 3 µm to avoid leakage


65 Primary function is retention
Primary function is exclusion



68 Lip Seals To minimize wear
The contact pressure should be as low as possible. Shaft surface should be smooth to µm. There must be enough fluid to form a hydrodynamic film Fluid pressure must be low (0-3 psi )

69 V-Seals

70 Flexi-Lip Rotary Seals
Speeds up to 5000 fps Pressures up to 150 psi Material: PTFE, graphite






76 Metallic Seals Metallic seals go where polymers cannot
High temperatures (Above 400 to 1800 Degree F) Cryogenic temperatures (below −238 °F) High pressures (3000 psi to psi) High speeds

77 Metal Seals

78 C-Ring and Energized C-Ring

79 E-Ring and O-Ring

80 U-Ring and Metal Wire

81 Combustion Engine Piston Rings
First compression ring (1) Second compression ring (2) Oil scraper ring (3)

82 Piston Rings Compression ring Wiper ring (secondary compression ring)
Seals the gases in the cylinder Gas pressure forces the ring against the cylinder wall Wiper ring (secondary compression ring) Seals the gases that escape the compression ring Wipes excess oil from cylinder wall Oil ring Made of two thin rails with slots Wipes excess oil from cylinder walls through port holes

83 Labyrinth Seals

84 Labyrinth Seal

85 Labyrinth Seal

86 Mechanical Seals Rotating Elements


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